We hope to identify the exact metabolic defect in the disease, "cystinosis". These studies will involve finding a better method to isolate pur lysosome preparations from cultured human cells. We then hope to use these lysosomes to study the fate of cystine and other amino acids in these organelles. For example, we have recently found that these organelles contain the major pool of free-amino acids that is present within normal mammalian cells. In addition we are developing methods for the isolation, identification and quantitation of any sulfhydryl or disulfide which occurs within the physiologic material. Additionally, we are involved in a large, double-blind study to evaluate the efficacy of cysteamine in patients with nephropathic cystinosis.